Pescadillo is required for Xenopus laevis eye development and neural crest migration

Comparing the effects of three neonicotinoids on embryogenesis of the South African clawed frog Xenopus laevis

Neonicotinoids (NEOs) are widely used insecticides that are ubiquitous in agricultural use. Since NEOs are found in natural waters as well as in tap water and human urine in regions where NEOs are widely used, NEOs pose a potential hazard to non-target organisms such as animals and humans. Some of the commonly detected NEOs are imidacloprid (IMD), thiamethoxam (TMX), and its metabolite clothianidin (CLO). Although previously published scientific information, including an assessment of the environmental risks, particularly for bees, had resulted in a ban on the outdoor use of these three NEOs in the EU - their use is now only permitted in closed greenhouses - these NEOs continue to be used in agriculture in many other parts of the world. Therefore, a detailed study and comparison of the effects of NEOs on the embryonic development of non-target organisms is needed to further define the risk profiles. Embryos of the South African clawed frog Xenopus laevis, a well-established aquatic model, were exposed to different concentrations of IMD, TMX, or CLO (0.1-100 mg/L) to study and compare the possible effects of a single contaminant in natural water bodies on early embryogenesis. The results included a reduced body length, a smaller orbital space, impaired cranial cartilage and nerves, and an altered heart structure and function. At the molecular level, NEO exposure partially resulted in an altered expression of tissue-specific factors, which are involved in eye, cranial placode, and heart development. Our results suggest that the NEOs studied negatively affect the embryonic development of the non-target organism X. laevis. Since pesticides, especially NEOs, pollute the environment worldwide, it is suggested that they are strictly controlled and monitored in the areas where they are used. In addition, the question arises as to whether pesticide metabolites also pose a risk to the environment and need to be investigated further so that they can be taken into account when registering ingredients.

Prdm15 acts upstream of Wnt4 signaling in anterior neural development of Xenopus laevis

Mutations in PRDM15 lead to a syndromic form of holoprosencephaly (HPE) known as the Galloway-Mowat syndrome (GAMOS). While a connection between PRDM15, a zinc finger transcription factor, and WNT/PCP signaling has been established, there is a critical need to delve deeper into their contributions to early development and GAMOS pathogenesis. We used the South African clawed frog Xenopus laevis as the vertebrate model organism and observed that prdm15 was enriched in the tissues and organs affected in GAMOS. Furthermore, we generated a morpholino oligonucleotide-mediated prdm15 knockdown model showing that the depletion of Prdm15 leads to abnormal eye, head, and brain development, effectively recapitulating the anterior neural features in GAMOS. An analysis of the underlying molecular basis revealed a reduced expression of key genes associated with eye, head, and brain development. Notably, this reduction could be rescued by the introduction of wnt4 RNA, particularly during the induction of the respective tissues. Mechanistically, our data demonstrate that Prdm15 acts upstream of both canonical and non-canonical Wnt4 signaling during anterior neural development. Our findings describe severe ocular and anterior neural abnormalities upon Prdm15 depletion and elucidate the role of Prdm15 in canonical and non-canonical Wnt4 signaling.

Bop1 is required to establish precursor domains of craniofacial tissues

Bop1 can promote cell proliferation and is a component of the Pes1-Bop1-WDR12 (PeBoW) complex that regulates ribosomal RNA processing and biogenesis. In embryos, however, bop1 mRNA is highly enriched in the neural plate, cranial neural crest and placodes, and potentially may interact with Six1, which also is expressed in these tissues. Recent work demonstrated that during development, Bop1 is required for establishing the size of the tadpole brain, retina and cranial cartilages, as well as controlling neural tissue gene expression levels. Herein, we extend this work by assessing the effects of Bop1 knockdown at neural plate and larval stages. Loss of Bop1 expanded neural plate gene expression domains (sox2, sox11, irx1) and reduced neural crest (foxd3, sox9), placode (six1, sox11, irx1, sox9) and epidermal (dlx5) expression domains. At larval stages, Bop1 knockdown reduced the expression of several otic vesicle genes (six1, pax2, irx1, sox9, dlx5, otx2, tbx1) and branchial arch genes that are required for chondrogenesis (sox9, tbx1, dlx5). The latter was not the result of impaired neural crest migration. Together these observations indicate that Bop1 is a multifunctional protein that in addition to its well-known role in ribosomal biogenesis functions during early development to establish the craniofacial precursor domains.

The impact of the insecticide acetamiprid on the embryogenesis of the aquatic model organism Xenopus laevis

Acetamiprid (ACT) is used extensively in agriculture worldwide, although data on ACT concentrations in natural water bodies and its impact on aquatic organisms are limited. To study whether ACT influences the embryogenesis of the South African clawed frog Xenopus laevis, embryos were incubated in ACT solutions from 0.01 to 100 mg/L. The low concentrations were chosen on the basis of concentrations already found in nature. ACT treatment leads to shorter embryo lengths, intestine malformation and reduced eye areas. It also affects the cranial cartilage and cardiac development as well as the embryo's mobility. The expression of tissue-specific marker genes is affected as well. Thus, our study suggests that pesticides may lead to an increased mortality of non-target organisms and emphasizes the importance of regular testing for ACT concentrations in nature. Our study provides an overview of ACT effects and can therefore be used as a basis for an ACT risk assessment.

Glyphosate without Co-formulants affects embryonic development of the south african clawed frog Xenopus laevis

BACKGROUND

Glyphosate (GLY) is the most widely used herbicide in the world. Due to its mode of action as an inhibitor of the 5-enolpyruvylshikimate-3-phosphate synthase, an important step in the shikimate pathway, specifically in plants, GLY is considered to be of low toxicity to non-target organisms. However, various studies have shown the negative effects of GLY on the mortality and development of different non-target organisms, including insects, rodents, fish and amphibians. To better understand the various effects of GLY in more detail, we studied the effects of GLY without co-formulants during the embryogenesis of the aquatic model organism Xenopus laevis.

RESULTS

A treatment with GLY affected various morphological endpoints in X. laevis tadpoles (body length, head width and area, eye area). Additionally, GLY interfered with the mobility as well as the neural and cardiac development of the embryos at stage 44/45. We were able to detect detailed structural changes in the cranial nerves and the heart and gained insights into the negative effects of GLY on cardiomyocyte differentiation.

CONCLUSION

The application of GLY without co-formulants resulted in negative effects on several endpoints in the early embryonic development of X. laevis at concentrations that are environmentally relevant and concentrations that reflect the worst-case scenarios. This indicates that GLY could have a strong negative impact on the survival and lives of amphibians in natural waters. As a result, future GLY approvals should consider its impact on the environment.

The neonicotinoid thiacloprid leads to multiple defects during early embryogenesis of the South African clawed frog (Xenopuslaevis)

There is increasing concern about the health effects of pesticides that pollute natural waters. In particular, the use of neonicotinoids, such as thiacloprid (THD), is causing unease. THD is considered non-toxic to non-target vertebrates. Studies classify THD as carcinogenic, toxic to reproduction, and therefore harmful to the environment. A detailed study of possible THD effects during the amphibian embryogenesis is needed because leaching can introduce THD into aquatic environments. We incubated stage 2 embryos of the South African clawed frog in various THD concentrations (0.1-100 mg/L) at 14 °C to study the potential effects of a one-time THD contamination of waters on the early embryogenesis. We showed that THD has, indeed, negative effects on the embryonic development of the X. laevis. A treatment with THD led to a reduced embryonic body length and mobility. Furthermore, a treatment with THD resulted in smaller cranial cartilages, eyes and brains, and the embryos had shorter cranial nerves and an impaired cardiogenesis. On a molecular basis, THD led to a reduced expression of the brain marker emx1 and the heart marker mhcα. Our results underly the importance of a strict and efficient monitoring of the regulatory levels and application areas of THD.

OTUD3: A Lys6 and Lys63 specific deubiquitinase in early vertebrate development

Ubiquitination and deubiquitylation regulate essential cellular processes and involve hundreds of sequentially acting enzymes, many of which are barely understood. OTUD3 is an evolutionarily highly conserved deubiquitinase involved in many aspects of cellular homeostasis. However, its biochemical properties and physiological role during development are poorly understood. Here, we report on the expression of OTUD3 in human tissue samples where it appears prominently in those of neuronal origin. In cells, OTUD3 is present in the cytoplasm where it can bind to microtubules. Interestingly, we found that OTUD3 cleaves preferentially at K6 and K63, i.e., poly-ubiquitin linkages that are not primarily involved in protein degradation. We employed Xenopus embryos to study the consequences of suppressing otud3 function during early neural development. We found that Otud3 deficiency led to impaired formation of cranial and particularly of cranial neural crest-derived structures as well as movement defects. Thus, OTUD3 appears as a neuronally enriched deubiquitinase that is involved in the proper development of the neural system.

Neural crest cells development and neuroblastoma progression: Role of Wnt signaling

Neuroblastoma (NB) is one of the most common heterogeneous extracranial cancers in infancy that arises from neural crest (NC) cells of the sympathetic nervous system. The Wnt signaling pathway, both canonical and noncanonical pathway, is a highly conserved signaling pathway that regulates the development and differentiation of the NC cells during embryogenesis. Reports suggest that aberrant activation of Wnt ligands/receptors in Wnt signaling pathways promote progression and relapse of NB. Wnt signaling pathways regulate NC induction and migration in a similar manner; it regulates proliferation and metastasis of NB. Inhibiting the Wnt signaling pathway or its ligands/receptors induces apoptosis and abrogates proliferation and tumorigenicity in all major types of NB cells. Here, we comprehensively discuss the Wnt signaling pathway and its mechanisms in regulating the development of NC and NB pathogenesis. This review highlights the implications of aberrant Wnt signaling in the context of etiology, progression, and relapse of NB. We have also described emerging strategies for Wnt-based therapies against the progression of NB that will provide new insights into the development of Wnt-based therapeutic strategies for NB.

Human pre-60S assembly factors link rRNA transcription to pre-rRNA processing

In eukaryotes, the nucleolus is the site of ribosome biosynthesis, an essential process in all cells. While human ribosome assembly is largely evolutionarily conserved, many of the regulatory details underlying its control and function have not yet been well-defined. The nucleolar protein RSL24D1 was originally identified as a factor important for 60S ribosomal subunit biogenesis. In addition, the PeBoW (BOP1-PES1-WDR12) complex has been well-defined as required for pre-28S rRNA processing and cell proliferation. In this study, we show that RSL24D1 depletion impairs both pre-ribosomal RNA (pre-rRNA) transcription and mature 28S rRNA production, leading to decreased protein synthesis and p53 stabilization in human cells. Surprisingly, each of the PeBoW complex members is also required for pre-rRNA transcription. We demonstrate that RSL24D1 and WDR12 co-immunoprecipitate with the RNA polymerase I subunit, RPA194, and regulate its steady state levels. These results uncover the dual role of RSL24D1 and the PeBoW complex in multiple steps of ribosome biogenesis, and provide evidence implicating large ribosomal subunit biogenesis factors in pre-rRNA transcription control.

Functions of block of proliferation 1 during anterior development in Xenopus laevis

Block of proliferation 1 (Bop1) is a nucleolar protein known to be necessary for the assembly of the 60S subunit of ribosomes. Here, we show a specific bop1 expression in the developing anterior tissue of the South African clawed frog Xenopus laevis. Morpholino oligonucleotide-mediated knockdown approaches demonstrated that Bop1 is required for proper development of the cranial cartilage, brain, and the eyes. Furthermore, we show that bop1 knockdown leads to impaired retinal lamination with disorganized cell layers. Expression of neural crest-, brain-, and eye-specific marker genes was disturbed. Apoptotic and proliferative processes, which are known to be affected during ribosomal biogenesis defects, are not hindered upon bop1 knockdown. Because early Xenopus embryos contain a large store of maternal ribosomes, we considered if Bop1 might have a role independent of de novo ribosomal biogenesis. At early embryonic stages, pax6 expression was strongly reduced in bop1 morphants and synergy experiments indicate a common signaling pathway of the two molecules, Bop1 and Pax6. Our studies imply a novel function of Bop1 independent of ribosomal biogenesis.

Cilia-localized GID/CTLH ubiquitin ligase complex regulates protein homeostasis of sonic hedgehog signaling components

Cilia are evolutionarily conserved organelles that orchestrate a variety of signal transduction pathways, such as sonic hedgehog (SHH) signaling, during embryonic development. Our recent studies have shown that loss of GID ubiquitin ligase function results in aberrant AMP-activated protein kinase (AMPK) activation and elongated primary cilia, which suggests a functional connection to cilia. Here, we reveal that the GID complex is an integral part of the cilium required for primary cilia-dependent signal transduction and the maintenance of ciliary protein homeostasis. We show that GID complex subunits localize to cilia in both Xenopus laevis and NIH3T3 cells. Furthermore, we report SHH signaling pathway defects that are independent of AMPK and mechanistic target of rapamycin (MTOR) activation. Despite correct localization of SHH signaling components at the primary cilium and functional GLI3 processing, we find a prominent reduction of some SHH signaling components in the cilium and a significant decrease in SHH target gene expression. Since our data reveal a critical function of the GID complex at the primary cilium, and because suppression of GID function in X. laevis results in ciliopathy-like phenotypes, we suggest that GID subunits are candidate genes for human ciliopathies that coincide with defects in SHH signal transduction.

The Ribosomal Protein L5 Functions During Xenopus Anterior Development Through Apoptotic Pathways

Ribosomal biogenesis is a fundamental process necessary for cell growth and division. Ribosomal protein L5 (Rpl5) is part of the large ribosomal subunit. Mutations in this protein have been associated with the congenital disease Diamond Blackfan anemia (DBA), a so called ribosomopathy. Despite of the ubiquitous need of ribosomes, clinical manifestations of DBA include tissue-specific symptoms, e.g., craniofacial malformations, eye abnormalities, skin pigmentation failure, cardiac defects or liver cirrhosis. Here, we made use of the vertebrate model organism Xenopus laevis and showed a specific expression of rpl5 in the developing anterior tissue correlating with tissues affected in ribosomopathies. Upon Rpl5 knockdown using an antisense-based morpholino oligonucleotide approach, we showed different phenotypes affecting anterior tissue, i.e., defective cranial cartilage, malformed eyes, and microcephaly. Hence, the observed phenotypes in Xenopus laevis resemble the clinical manifestations of DBA. Analyses of the underlying molecular basis revealed that the expression of several marker genes of neural crest, eye, and brain are decreased during induction and differentiation of the respective tissue. Furthermore, Rpl5 knockdown led to decreased cell proliferation and increased cell apoptosis during early embryogenesis. Investigating the molecular mechanisms underlying Rpl5 function revealed a more than additive effect between either loss of function of Rpl5 and loss of function of c-Myc or loss of function of Rpl5 and gain of function of Tp53, suggesting a common signaling pathway of these proteins. The co-injection of the apoptosis blocking molecule Bcl2 resulted in a partial rescue of the eye phenotype, supporting the hypothesis that apoptosis is one main reason for the phenotypes occurring upon Rpl5 knockdown. With this study, we are able to shed more light on the still poorly understood molecular background of ribosomopathies.

Impact of glyphosate-based herbicide on early embryonic development of the amphibian Xenopus laevis

BACKGROUND

Worldwide, amphibian populations are declining drastically. One reason might be the use of pesticides including herbicides. The herbicide glyphosate is an inhibitor of the 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase of the plant shikimate pathway, preventing the formation of aromatic amino acids and thus inducing plant death. Due to this specific action, GBH are considered nontoxic to non-target organisms. However, GBH impairs embryonic development of chickens, amphibians and fishes. So far, no detailed tissue- and organ-specific analysis of the effects of GBH during development in amphibians has been performed.

RESULTS

We demonstrated that GBH Roundup® LB plus has a negative effect on embryonic development of the South African clawed frog Xenopus laevis. GBH treatment with sublethal concentrations resulted in a reduced body length and mobility of embryos. Furthermore, incubation with GBH led to smaller eyes, brains and cranial cartilages in comparison to untreated embryos. GBH incubation also resulted in shorter cranial nerves and had an effect on cardiac development including reduced heart rate and atrium size. On a molecular basis, GBH treatment led to reduced expression of marker genes in different tissues and developmental stages.

CONCLUSION

GBH leads to disturbed embryonic development of Xenopus laevis.

Systematic mapping of rRNA 2'-O methylation during frog development and involvement of the methyltransferase Fibrillarin in eye and craniofacial development in Xenopus laevis

Ribosomes are essential nanomachines responsible for protein production. Although ribosomes are present in every living cell, ribosome biogenesis dysfunction diseases, called ribosomopathies, impact particular tissues specifically. Here, we evaluate the importance of the box C/D snoRNA-associated ribosomal RNA methyltransferase fibrillarin (Fbl) in the early embryonic development of Xenopus laevis. We report that in developing embryos, the neural plate, neural crest cells (NCCs), and NCC derivatives are rich in fbl transcripts. Fbl knockdown leads to striking morphological defects affecting the eyes and craniofacial skeleton, due to lack of NCC survival caused by massive p53-dependent apoptosis. Fbl is required for efficient pre-rRNA processing and 18S rRNA production, which explains the early developmental defects. Using RiboMethSeq, we systematically reinvestigated ribosomal RNA 2’-O methylation in X. laevis, confirming all 89 previously mapped sites and identifying 15 novel putative positions in 18S and 28S rRNA. Twenty-three positions, including 10 of the new ones, were validated orthogonally by low dNTP primer extension. Bioinformatic screening of the X. laevis transcriptome revealed candidate box C/D snoRNAs for all methylated positions. Mapping of 2’-O methylation at six developmental stages in individual embryos indicated a trend towards reduced methylation at specific positions during development. We conclude that fibrillarin knockdown in early Xenopus embryos causes reduced production of functional ribosomal subunits, thus impairing NCC formation and migration.

Ribosomes are essential nanomachines responsible for protein production in all cells. Ribosomopathies are diseases caused by improper ribosome formation due to mutations in ribosomal proteins or ribosome assembly factors. Such diseases primarily affect the brain and blood, and it is unclear how malfunctioning of a process as general as ribosome formation can lead to tissue-specific diseases. Here we have examined how fibrillarin, an enzyme which modifies ribosomal RNA by adding methyl groups at specific sites, affects early embryonic development in the frog Xenopus laevis. We have revealed its importance in the maturation of cells forming an embryonic structure called the neural crest. Fibrillarin depletion leads to reduced eye size and abnormal head shape, reminiscent of other conditions such as Treacher Collins syndrome. Molecularly, the observed phenotypes are explainable by increased p53-dependent programmed cell death triggered by inhibition of certain pre-rRNA processing steps. Our systematic investigation of the ribosomal RNA 2’-O methylation repertoire across development has further revealed hypomodification at a late stage of development, which might play a role in late developmental transitions involving differential translation by compositionally different ribosomes.

In Leishmania major, the Homolog of the Oncogene PES1 May Play a Critical Role in Parasite Infectivity

Leishmaniasis is a neglected tropical disease caused by Leishmania spp. The improvement of existing treatments and the discovery of new drugs remain ones of the major goals in control and eradication of this disease. From the parasite genome, we have identified the homologue of the human oncogene PES1 in Leishmania major (LmjPES). It has been demonstrated that PES1 is involved in several processes such as ribosome biogenesis, cell proliferation and genetic transcription. Our phylogenetic studies showed that LmjPES encodes a highly conserved protein containing three main domains: PES N-terminus (shared with proteins involved in ribosomal biogenesis), BRCT (found in proteins related to DNA repair processes) and MAEBL-type domain (C-terminus, related to erythrocyte invasion in apicomplexan). This gene showed its highest expression level in metacyclic promastigotes, the infective forms; by fluorescence microscopy assay, we demonstrated the nuclear localization of LmjPES protein. After generating mutant parasites overexpressing LmjPES, we observed that these clones displayed a dramatic increase in the ratio of cell infection within macrophages. Furthermore, BALB/c mice infected with these transgenic parasites exhibited higher footpad inflammation compared to those inoculated with non-overexpressing parasites.

Retinol binding protein 1 affects Xenopus anterior neural development via all-trans retinoic acid signaling

BACKGROUND

Retinol binding protein 1 (Rbp1) acts as an intracellular regulator of vitamin A metabolism and retinoid transport. In mice, Rbp1 deficiency decreases the capacity of hepatic stellate cells to take up all-trans retinol and sustain retinyl ester stores. Furthermore, Rbp1 is crucial for visual capacity. Although the function of Rbp1 has been studied in the mature eye, its role during early anterior neural development has not yet been investigated in detail.

RESULTS

We showed that rbp1 is expressed in the eye, anterior neural crest cells (NCCs) and prosencephalon of the South African clawed frog Xenopus laevis. Rbp1 knockdown led to defects in eye formation, including microphthalmia and disorganized retinal lamination, and to disturbed induction and differentiation of the eye field, as shown by decreased rax and pax6 expression. Furthermore, it resulted in reduced rax expression in the prosencephalon and affected cranial cartilage. Rbp1 inhibition also interfered with neural crest induction and migration, as shown by twist and slug. Moreover, it led to a significant reduction of the all-trans retinoic acid target gene pitx2 in NCC-derived periocular mesenchyme. The Rbp1 knockdown phenotypes were rescued by pitx2 RNA co-injection.

CONCLUSION

Rbp1 is crucial for the development of the anterior neural tissue.

Wnt Signaling in Neural Crest Ontogenesis and Oncogenesis

Neural crest (NC) cells are a temporary population of multipotent stem cells that generate a diverse array of cell types, including craniofacial bone and cartilage, smooth muscle cells, melanocytes, and peripheral neurons and glia during embryonic development. Defective neural crest development can cause severe and common structural birth defects, such as craniofacial anomalies and congenital heart disease. In the early vertebrate embryos, NC cells emerge from the dorsal edge of the neural tube during neurulation and then migrate extensively throughout the anterior-posterior body axis to generate numerous derivatives. Wnt signaling plays essential roles in embryonic development and cancer. This review summarizes current understanding of Wnt signaling in NC cell induction, delamination, migration, multipotency, and fate determination, as well as in NC-derived cancers.

The Wnt inhibitor Dkk1 is required for maintaining the normal cardiac differentiation program in Xenopus laevis

Wnt proteins can activate different intracellular signaling pathways. These pathways need to be tightly regulated for proper cardiogenesis. The canonical Wnt/β-catenin inhibitor Dkk1 has been shown to be sufficient to trigger cardiogenesis in gain-of-function experiments performed in multiple model systems. Loss-of-function studies however did not reveal any fundamental function for Dkk1 during cardiogenesis. Using Xenopus laevis as a model we here show for the first time that Dkk1 is required for proper differentiation of cardiomyocytes, whereas specification of cardiomyocytes remains unaffected in absence of Dkk1. This effect is at least in part mediated through regulation of non-canonical Wnt signaling via Wnt11. In line with these observations we also found that Isl1, a critical regulator for specification of the common cardiac progenitor cell (CPC) population, acts upstream of Dkk1.

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Dkk1 is required for cardiac development in Xenopus laevis.

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The Wnt inhibitor Dkk1 acts downstream of Isl1 during cardiac development in vivo.

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Loss of Dkk1 has no impact on cardiac specification in Xenopus.

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Normal cardiac differentiation is impaired upon Dkk1 inhibition in Xenopus.

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Dkk1 regulates canonical Wnt/β-catenin signaling during Xenopus cardiogenesis.

PES1 promotes the occurrence and development of papillary thyroid cancer by upregulating the ERα/ERβ protein ratio

PES1, a BRCT domain-containing protein, has been shown to play a role in modulating the balance and ratio between ERα and ERβ protein, which is involved in the occurrence and development of breast and ovarian cancer. However, its role in connection with the balance and ratio between ERα and ERβ protein in papillary thyroid cancer (PTC) remains unclear. Here, we found that ERα and ERβ were co-expressed in human PTC tissues and cells. ERα promoted and ERβ inhibited the proliferation, invasion and migration of PTC cells. PES1 modulated the balance between ERα and ERβ by elevating the ERα protein level and simultaneously reducing the ERβ protein level, then upregulating the ERα/ERβ protein ratio and promoting the proliferation, invasion and migration of PTC cells. In PTC tissues, PES1 protein level was positively correlated with the ERα protein level and negatively correlated with the ERβ protein level. The PES1 and ERα protein levels were gradually increased and the ERβ protein level was decreased by degree in the occurrence and development of PTC. Increased PES1 and ERα protein levels and decreased ERβ protein level were correlated with the aggressive behaviors of PTC patients such as large tumor size, extrathyroidal extension (ETE), lymph node metastasis (LNM), high BRAFV600E expression and high TNM stage. It is suggested that PES1 promotes the occurrence and development of PTC by elevating the ERα protein level and reducing the ERβ protein level, and then upregulating the ERα/ERβ protein ratio.

Nosip functions during vertebrate eye and cranial cartilage development

BACKGROUND

The nitric oxide synthase interacting protein (Nosip) has been associated with diverse human diseases including psychological disorders. In line, early neurogenesis of mouse and Xenopus is impaired upon Nosip deficiency. Nosip knockout mice show craniofacial defects and the down-regulation of Nosip in the mouse and Xenopus leads to microcephaly. Until now, the exact underlying molecular mechanisms of these malformations were still unknown.

RESULTS

Here, we show that nosip is expressed in the developing ocular system as well as the anterior neural crest cells of Xenopus laevis. Furthermore, Nosip inhibition causes severe defects in eye formation in the mouse and Xenopus. Retinal lamination as well as dorso-ventral patterning of the retina were affected in Nosip-depleted Xenopus embryos. Marker gene analysis using rax, pax6 and otx2 reveals an interference with the eye field induction and differentiation. A closer look on Nosip-deficient Xenopus embryos furthermore reveals disrupted cranial cartilage structures and an inhibition of anterior neural crest cell induction and migration shown by twist, snai2, and egr2. Moreover, foxc1 as downstream factor of retinoic acid signalling is affected upon Nosip deficiency.

CONCLUSIONS

Nosip is a crucial factor for the development of anterior neural tissue such the eyes and neural crest cells. Developmental Dynamics 247:1070-1082, 2018. © 2018 Wiley Periodicals, Inc.

Of Wnts and Ribosomes

Wnt proteins are secreted glycoproteins that activate different intracellular signal transduction pathways. They regulate cell proliferation and are required for proper embryonic development. Misregulation of Wnt signaling can result in various diseases including cancer. In most circumstances, cell growth is essential for cell division and thus cell proliferation. Therefore, several reports have highlighted the key role of Wnt proteins for cell growth. Ribosomes represent the cellular protein synthesis machinery and cells need to be equipped with an appropriate number of ribosomes to allow cell growth. Recent findings suggest a role for Wnt proteins in regulating ribosome biogenesis and we here summarize these findings representing a previously unknown function of Wnt proteins. Understanding this role of Wnt signaling might open new avenues to slow down proliferation by drugs for instance in cancer therapy.

Frizzled 3 acts upstream of Alcam during embryonic eye development

Formation of a functional eye during vertebrate embryogenesis requires different processes such as cell differentiation, cell migration, cell-cell interactions as well as intracellular signalling processes. It was previously shown that the non-canonical Wnt receptor Frizzled 3 (Fzd3) is required for proper eye formation, however, the underlying mechanism is poorly understood. Here we demonstrate that loss of Fzd3 induces severe malformations of the developing eye and that this defect is phenocopied by loss of the activated leukocyte cell adhesion molecule (Alcam). Promoter analysis revealed the presence of a Fzd3 responsive element within the alcam promoter, which is responsible for alcam expression during anterior neural development. In-depth analysis identified the jun N-terminal protein kinase 1 (JNK1) and the transcription factor paired box 2 (Pax2) to be important for the activation of alcam expression. Altogether our study reveals that alcam is activated through non-canonical Wnt signalling during embryonic eye development in Xenopus laevis and shows that this pathway plays a similar role in different tissues.

Direct nkx2-5 transcriptional repression of isl1 controls cardiomyocyte subtype identity

During cardiogenesis, most myocytes arise from cardiac progenitors expressing the transcription factors Isl1 and Nkx2-5. Here, we show that a direct repression of Isl1 by Nkx2-5 is necessary for proper development of the ventricular myocardial lineage. Overexpression of Nkx2-5 in mouse embryonic stem cells (ESCs) delayed specification of cardiac progenitors and inhibited expression of Isl1 and its downstream targets in Isl1(+) precursors. Embryos deficient for Nkx2-5 in the Isl1(+) lineage failed to downregulate Isl1 protein in cardiomyocytes of the heart tube. We demonstrated that Nkx2-5 directly binds to an Isl1 enhancer and represses Isl1 transcriptional activity. Furthermore, we showed that overexpression of Isl1 does not prevent cardiac differentiation of ESCs and in Xenopus laevis embryos. Instead, it leads to enhanced specification of cardiac progenitors, earlier cardiac differentiation, and increased cardiomyocyte number. Functional and molecular characterization of Isl1-overexpressing cardiomyocytes revealed higher beating frequencies in both ESC-derived contracting areas and Xenopus Isl1-gain-of-function hearts, which associated with upregulation of nodal-specific genes and downregulation of transcripts of working myocardium. Immunocytochemistry of cardiomyocyte lineage-specific markers demonstrated a reduction of ventricular cells and an increase of cells expressing the pacemaker channel Hcn4. Finally, optical action potential imaging of single cardiomyocytes combined with pharmacological approaches proved that Isl1 overexpression in ESCs resulted in normally electrophysiologically functional cells, highly enriched in the nodal subtype at the expense of the ventricular lineage. Our findings provide an Isl1/Nkx2-5-mediated mechanism that coordinately regulates the specification of cardiac progenitors toward the different myocardial lineages and ensures proper acquisition of myocyte subtype identity.

An Epha4/Sipa1l3/Wnt pathway regulates eye development and lens maturation

The signal-induced proliferation associated family of proteins comprises four members, SIPA1 and SIPA1L1-1L3. Mutations of the human SIPA1L3 gene result in congenital cataracts. In Xenopus, loss of Sipa1l3 function led to a severe eye phenotype that was distinguished by smaller eyes and lenses including lens fiber cell maturation defects. We found a direct interaction between Sipa1l3 and Epha4, building a functional platform for proper ocular development. Epha4 deficiency phenocopied loss of Sipa1l3 and rescue experiments demonstrated that Epha4 acts up-stream of Sipa1l3 during eye development. Both, Sipa1l3 and Epha4 are required for early eye specification. The ocular phenotype, upon loss of either Epha4 or Sipa1l3, was partially mediated by rax. We demonstrated that canonical Wnt signaling is inhibited downstream of Epha4/Sipa1l3 during normal eye development. Depletion of either Sipa1l3 or Epha4 resulted in an up-regulation of axin2 expression, a direct Wnt/β-catenin target gene. In line with this, Sipa1l3 or Epha4 depletion could be rescued by blocking Wnt/β-catenin or activating non-canonical Wnt signaling. We therefore conclude that this pathomechanism prevents proper eye development and maturation of lens fiber cells resulting in congenital cataracts.

Nucleolar protein PES1 is a marker of neuroblastoma outcome and is associated with neuroblastoma differentiation

Neuroblastoma (NB) is a childhood malignant tumor that arises from precursor cells of the sympathetic nervous system. Spontaneous regression is a phenomenon unique to NBs and is caused by differentiation of tumor cells. PES1 is a multifunctional protein with roles in both neural development and ribosome biogenesis. Various kinds of models have revealed the significance of PES1 in neurodevelopment. However, the roles of PES1 in NB tumorigenesis and differentiation have remained unknown. Here we show that NB cases with MYCN amplification and clinically unfavorable stage (INSS stage 4) express higher levels of PES1. High PES1 expression was associated with worse overall and relapse-free survival. In NB cell lines, PES1 knockdown suppressed tumor cell growth and induced apoptosis. This growth inhibition was associated with the expression of NB differentiation markers. However, when the differentiation of NB cell lines was induced by the use of all-trans retinoic acid, there was a corresponding decrease in PES1 expression. Pes1 expression of tumorspheres originated from MYCN transgenic mice also diminished after the induction of differentiation with growth factors. We also reanalyzed the distribution of PES1 in the nucleolus. PES1 was localized in the dense fibrillar component, but not in the granular component of nucleoli. After treatment with the DNA-damaging agent camptothecin, this distribution was dramatically changed to diffuse nucleoplasmic. These data suggest that PES1 is a marker of NB outcome, that it regulates NB cell proliferation, and is associated with NB differentiation.

The Wnt/JNK signaling target gene alcam is required for embryonic kidney development

Proper development of nephrons is essential for kidney function. β-Catenin-independent Wnt signaling through Fzd8, Inversin, Daam1, RhoA and Myosin is required for nephric tubule morphogenesis. Here, we provide a novel mechanism through which non-canonical Wnt signaling contributes to tubular development. Using Xenopus laevis as a model system, we found that the cell-adhesion molecule Alcam is required for proper nephrogenesis and functions downstream of Fzd3 during embryonic kidney development. We found alcam expression to be independent of Fzd8 or Inversin, but to be transcriptionally regulated by the β-Catenin-independent Wnt/JNK pathway involving ATF2 and Pax2 in a direct manner. These novel findings indicate that several branches of Wnt signaling are independently required for proximal tubule development. Moreover, our data indicate that regulation of morphogenesis by non-canonical Wnt ligands also involves direct transcriptional responses in addition to the effects on a post-translational level.

Pescadillo plays an essential role in plant cell growth and survival by modulating ribosome biogenesis

Pescadillo (PES) is involved in diverse cellular processes such as embryonic development, ribosomal biogenesis, cell proliferation, and gene transcription in yeast and metazoans. In this study, we characterized cellular functions of plant PES in Nicotiana benthamiana, Arabidopsis, and tobacco BY-2 cells. A GFP fusion protein of PES is predominantly localized in the nucleolus, where its localization requires the N-terminal domain of PES. Silencing of plant PES led to growth arrest and acute cell death. PES interacts with plant homologs of BOP1 and WDR12 in the nucleolus, which are also nucleolar proteins involved in ribosome biogenesis of yeast and mammals. PES, BOP1, and WDR12 cofractionated with ribosome subunits. Depletion of any of these proteins led to defective biogenesis of the 60S ribosome large subunits and disruption of nucleolar morphology. PES-deficient plant cells also exhibited delayed maturation of 25S ribosomal RNA and suppressed global translation. During mitosis in tobacco BY-2 cells, PES is associated with the mitotic microtubules, including spindles and phragmoplasts, and PES deficiency disrupted spindle organization and chromosome arrangement. Collectively, these results suggest that plant PES has an essential role in cell growth and survival through its regulation of ribosome biogenesis and mitotic progression.

sox4 and sox11 function during Xenopus laevis eye development

SoxC genes are involved in many developmental processes such as cardiac, lymphoid, and bone development. The SoxC gene family is represented by Sox4, Sox11, and Sox12. Loss of either Sox4 or Sox11 function is lethal during mouse embryogenesis. Here, we demonstrate that sox4 and sox11 are strongly expressed in the developing eye, heart as well as brain in Xenopus laevis. Morpholino oligonucleotide mediated knock-down approaches in anterior neural tissue revealed that interference with either Sox4 or Sox11 function affects eye development. A detailed analysis demonstrated strong effects on eye size and retinal lamination. Neural induction was unaffected upon Sox4 or Sox11 MO injection and early eye field differentiation and cell proliferation were only mildly affected. Depletion of both genes, however, led independently to a significant increase in cell apoptosis in the eye. In summary, Sox4 and Sox11 are required for Xenopus visual system development.

Calponin 2 acts as an effector of noncanonical Wnt-mediated cell polarization during neural crest cell migration

Neural crest cells (NCCs) migrate throughout the embryo to differentiate into cell types of all germ layers. Initial directed NCC emigration relies on planar cell polarity (PCP), which through the activity of the small GTPases RhoA and Rac governs the actin-driven formation of polarized cell protrusions. We found that the actin binding protein calponin 2 (Cnn2) was expressed in protrusions at the leading edge of migratory NCCs in chicks and frogs. Cnn2 knockdown resulted in NCC migration defects in frogs and chicks and randomized outgrowth of cell protrusions in NCC explants. Morphant cells showed central stress fibers at the expense of the peripheral actin network. Cnn2 acted downstream of Wnt/PCP, as migration defects induced by dominant-negative Wnt11 or inhibition of RhoA function were rescued by Cnn2 knockdown. These results suggest that Cnn2 modulates actin dynamics during NCC migration as an effector of noncanonical Wnt/PCP signaling.

Ribosomal biogenesis genes play an essential and p53-independent role in zebrafish pancreas development

Mutations in the human Shwachman-Bodian-Diamond syndrome (SBDS) gene cause defective ribosome assembly and are associated with exocrine pancreatic insufficiency, chronic neutropenia and skeletal defects. However, the mechanism underlying these phenotypes remains unclear. Here we show that knockdown of the zebrafish sbds ortholog fully recapitulates the spectrum of developmental abnormalities observed in the human syndrome, and further implicate impaired proliferation of ptf1a-expressing pancreatic progenitor cells as the basis for the observed pancreatic phenotype. It is thought that diseases of ribosome assembly share a p53-dependent mechanism. However, loss of p53 did not rescue the developmental defects associated with loss of zebrafish sbds. To clarify the molecular mechanisms underlying the observed organogenesis defects, we performed transcriptional profiling to identify candidate downstream mediators of the sbds phenotype. Among transcripts displaying differential expression, functional group analysis revealed marked enrichment of genes related to ribosome biogenesis, rRNA processing and translational initiation. Among these, ribosomal protein L3 (rpl3) and pescadillo (pes) were selected for additional analysis. Similar to knockdown of sbds, knockdown or mutation of either rpl3 or pes resulted in impaired expansion of pancreatic progenitor cells. The pancreatic phenotypes observed in rpl3- and pes-deficient embryos were also independent of p53. Together, these data suggest novel p53-independent roles for ribosomal biogenesis genes in zebrafish pancreas development.

Mutation of pescadillo disrupts oligodendrocyte formation in zebrafish

Background

In vertebrates, the myelin sheath is essential for efficient propagation of action potentials along the axon shaft. Oligodendrocytes are the cells of the central nervous system that create myelin sheaths. During embryogenesis, ventral neural tube precursors give rise to oligodendrocyte progenitor cells, which divide and migrate throughout the central nervous system. This study aimed to investigate mechanisms that regulate oligodendrocyte progenitor cell formation.

Methodology/Principal Findings

By conducting a mutagenesis screen in transgenic zebrafish, we identified a mutation, designated vu166, by an apparent reduction in the number of oligodendrocyte progenitor cells in the dorsal spinal cord. We subsequently determined that vu166 is an allele of pescadillo, a gene known to play a role in ribosome biogenesis and cell proliferation. We found that pescadillo function is required for both the proper number of oligodendrocyte progenitors to form, by regulating cell cycle progression, and for normal levels of myelin gene expression.

Conclusions/Significance

Our data provide evidence that neural precursors require pes function to progress through the cell cycle and produce oligodendrocyte progenitor cells and for oligodendrocyte differentiation.

Pescadillo homologue 1 and Peter Pan function during Xenopus laevis pronephros development

BACKGROUND INFORMATION

pes1 (pescadillo homologue 1) and ppan (Peter Pan) are multifunctional proteins involved in ribosome biogenesis, cell proliferation, apoptosis, cell migration and regulation of gene expression. Both proteins are required for early neural development in Xenopus laevis, as previously demonstrated.

RESULTS

We show that the expression of both genes in the developing pronephros depends on wnt4 and fzd3 (frizzled homologue 3) function. Loss of pes1 or ppan by MO (morpholino oligonucleotide)-based knockdown approaches resulted in strong malformations during pronephric tubule formation. Defects were already notable during specification of pronephric progenitor cells, as shown by lhx1 expression. Moreover, we demonstrated that Xenopus pes1 and ppan interact physically and functionally and that pes1 and ppan can cross-rescue the loss of function phenotype of one another. Interference with rRNA synthesis, however, did not result in a similar early pronephros phenotype.

CONCLUSION

These results demonstrate that pes1 and ppan are required for Xenopus pronephros development and indicate that their function in the pronephros is independent of their role in ribosome biosynthesis.

Peter Pan functions independently of its role in ribosome biogenesis during early eye and craniofacial cartilage development in Xenopus laevis

The Xenopus oocyte possesses a large maternal store of ribosomes, thereby uncoupling early development from the de novo ribosome biosynthesis required for cell growth. Brix domain-containing proteins, such as Peter Pan (PPan), are essential for eukaryotic ribosome biogenesis. In this study, we demonstrate that PPan is expressed maternally as well as in the eye and cranial neural crest cells (NCCs) during early Xenopus laevis development. Depletion of PPan and interference with rRNA processing using antisense morpholino oligonucleotides resulted in eye and cranial cartilage malformations. Loss of PPan, but not interference with rRNA processing, led to an early downregulation of specific marker genes of the eye, including Rx1 and Pax6, and of NCCs, such as Twist, Slug and FoxD3. We found that PPan protein is localized in the nucleoli and mitochondria and that loss of PPan results in increased apoptosis. These findings indicate a novel function of PPan that is independent of its role in ribosome biogenesis.

Expression analysis of epb41l4a during Xenopus laevis embryogenesis

Epbl41l4a (erythrocyte protein band 4.1-like 4a, also named Nbl4) is a member of the band 4.1/Nbl4 (novel band 4.1-like protein 4) group of the FERM (4.1, ezrin, radixin, moesin) protein superfamily. Proteins encoded by this gene family are involved in many cellular processes such as organization of epithelial cells and signal transduction. On a molecular level, band 4.1/Nbl4 proteins have been shown to link membrane-associated proteins and lipids to the actin cytoskeleton. Epbl41l4a has also recently been identified as a target gene of the Wnt/β-catenin pathway. Here, we describe for the first time the spatio-temporal expression of epbl41l4a using Xenopus laevis as a model system. We observed a strong and specific expression of epb41l4a in the developing somites, in particular during segmentation as well as in the nasal and cranial placodes, pronephros, and neural tube. Thus, epbl41l4a is expressed in tissues undergoing morphogenetic movements, suggesting a functional role of epbl41l4a during these processes.

Biology-oriented synthesis of a natural-product inspired oxepane collection yields a small-molecule activator of the Wnt-pathway

In Biology Oriented Synthesis the scaffolds of biologically relevant compound classes inspire the synthesis of focused compound collections enriched in bioactivity. This criterion is met by the structurally complex scaffolds of natural products (NPs) selected in evolution. The synthesis of NP-inspired compound collections approaching the complexity of NPs calls for the development of efficient synthetic methods. We have developed a one pot 4-7 step synthesis of mono-, bi-, and tricyclic oxepanes that resemble the core scaffolds of numerous NPs with diverse bioactivities. This sequence entails a ring-closing ene-yne metathesis reaction as key step and makes productive use of polymer-immobilized scavenger reagents. Biological profiling of a corresponding focused compound collection in a reporter gene assay monitoring for Wnt-signaling modulation revealed active Wntepanes. This unique class of small-molecule activators of the Wnt pathway modulates the van-Gogh-like receptor proteins (Vangl), which were previously identified in noncanonical Wnt signaling, and acts in synergy with the canonical activator protein (Wnt-3a).

p53 coordinates cranial neural crest cell growth and epithelial-mesenchymal transition/delamination processes

Neural crest development involves epithelial-mesenchymal transition (EMT), during which epithelial cells are converted into individual migratory cells. Notably, the same signaling pathways regulate EMT function during both development and tumor metastasis. p53 plays multiple roles in the prevention of tumor development; however, its precise roles during embryogenesis are less clear. We have investigated the role of p53 in early cranial neural crest (CNC) development in chick and mouse embryos. In the mouse, p53 knockout embryos displayed broad craniofacial defects in skeletal, neuronal and muscle tissues. In the chick, p53 is expressed in CNC progenitors and its expression decreases with their delamination from the neural tube. Stabilization of p53 protein using a pharmacological inhibitor of its negative regulator, MDM2, resulted in reduced SNAIL2 (SLUG) and ETS1 expression, fewer migrating CNC cells and in craniofacial defects. By contrast, electroporation of a dominant-negative p53 construct increased PAX7(+) SOX9(+) CNC progenitors and EMT/delamination of CNC from the neural tube, although the migration of these cells to the periphery was impaired. Investigating the underlying molecular mechanisms revealed that p53 coordinates CNC cell growth and EMT/delamination processes by affecting cell cycle gene expression and proliferation at discrete developmental stages; disruption of these processes can lead to craniofacial defects.

The spatio-temporal expression of ProSAP/shank family members and their interaction partner LAPSER1 during Xenopus laevis development

Members of the ProSAP/Shank family are important scaffolding proteins of the postsynaptic density (PSD). We investigated for the first time the expression of the three family members named Shank1, ProSAP1/Shank2, and ProSAP2/Shank3 during Xenopus laevis development. Shank1 is expressed in the neural tube, the retina, and the cranial ganglions. In contrast, ProSAP1/Shank2 transcripts could be visualized in the otic vesicle, the pronephros, the liver, the neural tube, and the retina. ProSAP2/Shank3 could be detected in the cardiovascular network, the neural tube, the pronephros, and the retina. Furthermore, we showed that LAPSER1 interacts with all three ProSAP/Shank family members in Xenopus embryos and co-localizes with ProSAP/Shank in a cell-based assay. In Xenopus, LAPSER1 is expressed in somites, brain, proctodeum, pronephros, and in some cranial ganglions. Thus, we suggest that members of the ProSAP/Shank family and LAPSER1 not only play a role in PSD formation and plasticity, but also during embryonic development.

Mechanism of Xenopus cranial neural crest cell migration

This review focuses on recent advances in the field of cranial neural crest cell migration in Xenopus laevis with specific emphasis on cell adhesion and the regulation of cell migration. Our goal is to combine the understanding of cell adhesion to the extracellular matrix with the regulation of cell-cell adhesion and the involvement of the planar cell polarity signaling-pathway in guiding the migration of cranial neural crest cells during embryogenesis.

Mechanisms driving neural crest induction and migration in the zebrafish and Xenopus laevis

The neural crest is an evolutionary adaptation, with roots in the formation of mesoderm. Modification of neural crest behavior has been is critical for the evolutionary diversification of the vertebrates and defects in neural crest underlie a range of human birth defects. There has been a tremendous increase in our knowledge of the molecular, cellular, and inductive interactions that converge on defining the neural crest and determining its behavior. While there is a temptation to look for simple models to explain neural crest behavior, the reality is that the system is complex in its circuitry. In this review, our goal is to identify the broad features of neural crest origins (developmentally) and migration (cellularly) using data from the zebrafish (teleost) and Xenopus laevis (tetrapod amphibian) in order to illuminate where general mechanisms appear to be in play, and equally importantly, where disparities in experimental results suggest areas of profitable study.

The multiple phases and faces of wnt signaling during cardiac differentiation and development

Understanding heart development on a molecular level is a prerequisite for uncovering the causes of congenital heart diseases. Therapeutic approaches that try to enhance cardiac regeneration or that involve the differentiation of resident cardiac progenitor cells or patient-specific induced pluripotent stem cells will also benefit tremendously from this knowledge. Wnt proteins have been shown to play multiple roles during cardiac differentiation and development. They are extracellular growth factors that activate different intracellular signaling branches. Here, we summarize our current understanding of how these factors affect different aspects of cardiogenesis, starting from early specification of cardiac progenitors and continuing on to later developmental steps, such as morphogenetic processes, valve formation, and establishment of the conduction system.

FMR1/FXR1 and the miRNA pathway are required for eye and neural crest development

FMR1 and FXR1 are RNA binding proteins interacting with the miRNA-induced silencing complex, RISC. Here we describe for the first time the function of these proteins during eye and neural crest (NC) development in Xenopus laevis. A loss of FMR1 or FXR1 results in abnormal eye development as well as defects in cranial cartilage derived from cranial NC cells. We further investigated the possible mechanism of these phenotypes by showing that a depletion of Dicer, an important enzyme for generating all mature miRNAs, in the anterior neural tissue also leads to eye and cranial cartilage defects. Furthermore, we examined the function of 12 miRNAs during anterior neural development. We show a specific requirement of six selected miRNAs during eye and cranial cartilage development. Mir-130a, -219, and -23b are involved in eye formation only whereas loss of miR-200b, miR-96 and miR-196a results in strong defects during eye as well as cranial cartilage development. Our results suggest an essential role for FMR1 and FXR1 for eye and NC development in X.laevis likely through an interaction with the miRNA pathway.

Eye field specification in Xenopus laevis

Vertebrate eyes begin as a small patch of cells at the most anterior end of the early brain called the eye field. If these cells are removed from an amphibian embryo, the eyes do not form. If the eye field is transplanted to another location on the embryo or cultured in a dish, it forms eyes. These simple cut and paste experiments were performed at the beginning of the last century and helped to define the embryonic origin of the vertebrate eye. The genes necessary for eye field specification and eventual eye formation, by contrast, have only recently been identified. These genes and the molecular mechanisms regulating the initial formation of the Xenopus laevis eye field are the subjects of this review.

Down-regulation of pescadillo inhibits proliferation and tumorigenicity of breast cancer cells

Pescadillo, which has been found to be involved in the process of ribosomal biogenesis, has been demonstrated to play a role in embryonic development, DNA replication, and gene transcription. While deregulation of ribosomal biogenesis was also found to contribute to carcinogenesis, and proteins that regulate ribosomal biogenesis are commonly overexpressed in primary tumors, little is known about the clinical significance and biological function of pescadillo in human breast cancer. In the current study, we found that the expression of pescadillo was markedly up-regulated in human breast cancer cells and tissues at both mRNA and protein levels. Immunohistochemical analysis revealed that pescadillo expression in clinical stage I-IV primary breast cancer tissues was statistically significantly higher than that in normal breast tissues (P < 0.05). Furthermore, we demonstrated that knockdown pescadillo with RNAis inhibited cell proliferation and the colony-forming ability of the cells. Anchorage-independent growth ability assay indicated that ablation of pescadillo led to the reduction of breast cancer cells tumorigenicity in vitro. Moreover, depletion of endogenous pescadillo resulted in decreased expression of cell cycle protein cyclin D1 and up-regulation of cyclin-dependent kinase inhibitor p27(Kip1), as well as attenuated protein kinase B (Akt)/glycogen synthase kinase 3 beta (GSK-3beta) signaling. Taken together, our results suggest that pescadillo might play a role in promoting the proliferation and carcinogenesis of human breast cancer, and thereby might be a potential target for human breast cancer treatment.

Repulsive guidance molecule A (RGM A) and its receptor neogenin during neural and neural crest cell development of Xenopus laevis

BACKGROUND INFORMATION

RGM A (repulsive guidance molecule A) is a GPI (glycosylphosphatidylinositol)-anchored glycoprotein which has repulsive properties on axons due to the interaction with its receptor neogenin. In addition, RGM A has been demonstrated to function as a BMP (bone morphogenetic protein) co-receptor.

RESULTS

In the present study, we provide the first analysis of early RGM A and neogenin expression and function in Xenopus laevis neural development. Tissue-specific RGM A expression starts at stage 12.5 in the anterior neural plate. Loss-of-function analyses suggest a function of RGM A and neogenin in regulating anterior neural marker genes, as well as eye development and neural crest cell migration. Furthermore, overexpression of RGM A leads to ectopic expression of neural crest cell marker genes.

CONCLUSIONS

These data indicate that RGM A and neogenin have important functions during early neural development, in addition to their role during axonal guidance and synapse formation.